1. Field of the Invention
The present invention relates to a sensitivity adjustment device and a radio wave communication device to which the sensitivity adjustment device is applied.
2. Description of the Related Art
In recent years, there have been spread of methods for transmitting and receiving (communicating) various data between electronic devices such as watches each having a wireless communication function, for example, to exchange data between the electronic devices, and to synchronize information therebetween, by a wireless system.
It is possible that data transmitted and received by wireless communications includes many pieces of personal information. Hence, it is necessary to accurately transmit/receive data from a particular electronic device to another particular electronic device in order to protect personal privacy or the like.
However, when there is a plurality of electronic devices around a user, it is possible that an electronic device of the user (main electronic device) cannot have wireless communications with another electronic device with which the main electronic device intends to have the wireless communications (intended electronic device) because the main electronic device causes interference with another electronic device with which the main electronic device does not intend to have the wireless communications (unintended electronic device). In particular, when communications are made in accordance with Bluetooth® which handles radio waves having a long wavelength, the radio waves are not blocked by obstacles, and hence a main electronic device easily causes interference with an unintended electronic device.
Conventionally, as a method for a main electronic device to appropriately establish pairing (namely, an initial registration operation) with an intended electronic device in a wireless communication system, avoiding interference from an unintended electronic device, for example, Japanese Patent Application Laid-Open Publication (Translation of PCT Application) No. 2007-536852 proposes disposing electronic devices (a main electronic device and an intended electronic device), which are desired to establish pairing with each other, close to each other, and making a query signal having an electric power level limited to being smaller than the standard signal output electric power level in a wireless communication system transmitted from one of the electronic devices, making an answer signal for the query signal transmitted from the other thereof when the other thereof detects the query signal, and starting a point-to-point connection between the electronic devices based on a fact that the other thereof answers the query signal first.
When pairing is performed by such a method, a main electronic device can establish pairing only with an intended electronic device, avoiding causing interference with an unintended electronic device.
However, the method requires disposing the electronic devices, which are desired to establish pairing with each other, close to each other or the like. This is troublesome to the user. In addition, there is a situation where the location of an intended electronic device for pairing is not known. That is, it is not always possible to dispose electronic devices, which are desired to establish pairing with each other, close to each other.
In order to avoid causing interference with an unintended electronic device, it is possible to lower sensitivity of an antenna of a main electronic device so as not to establish communication with an unintended electronic device.
However, electronic devices transmit and receive data therebetween for various purposes. There are other cases than the case where electronic devices are disposed close to each other to the extent of contacting with each other so as to communicate with each other for pairing or the like. For example, electronic devices having a short distance therebetween transmit/receive various data therebetween, the electronic devices being a portable terminal device and a watch or the like both of which a user wears. Furthermore, electronic devices expected to have some distance therebetween transmit/receive data therebetween, for example, so as to find whereabouts of one of the electronic devices, the one which a user has left somewhere (search function).
As for the former case, it is desirable to lower the sensitivity of the main electronic device because if the sensitivity thereof is too high, many electronic devices communicable with the main electronic device exist in a reception region, and consequently, it becomes difficult for the main electronic device to find an intended electronic device. On the other hand, as for the latter case, if the sensitivity thereof is low, the search function cannot be appropriately executed.
Therefore, it is required that the sensitivity of an electronic device to radio waves is changed in accordance with its purpose, use, state or the like when the electronic device transmits/receives data to/from another electronic device.
In a mobile phone, a personal computer or the like, the sensitivity is changed in a communication-related module such as a reception circuit.
In a small electronic device such as a watch, space to accommodate a battery is limited, and hence it is important to keep electric power consumption as low as possible. However, with the method described above, the electric power consumption in a communication-related module is high.
In addition, in the case where the sensitivity (reception) is changed in a communication-related module, the internal mechanism of the module or the like becomes complicated, and consequently, the shock-resistance or the like may be limited.